Polymer-Based Piping Systems in the CPI

7/21/2019 Polymer-Based Piping Systems in the CPI

http://slidepdf.com/reader/full/polymer-based-piping-systems-in-the-cpi 1/5

Polymeric piping systems havebeen used in well-defined seg-ments of the chemical processindustries (CPI) for decades.

They have proven their sustainabilityto manage almost any chemical loadup to temperatures of 100°C in themoderate pressure region ( p < 10 bar)if the choice of the respective piping-system material has been made cor-rectly. However, their potential of ex-

ceptional performance is still not fullyreflected by the number of polymer-based piping systems used in the CPI.

This article gives a comprehensivereview of the advantages and limita-tions of polymer-based piping systemsin the CPI. By also quoting represen-tative case studies as well as outlin-ing trends, aspects for further discus-sions for this topic are given withoutdevaluating possible non-polymericmaterial alternatives.

State of the artPiping systems become relevant where(mostly) liquid or gaseous media areconveyed, distributed, dosed or stored.Starting with their introduction about50 years ago, polymer-based pipingsystems have been fully establishedin many segments, such as buildingtechnology, gas and water supply [1].However, in many industrial sectorsof the CPI their application requiresa much more distinct consideration,as the transported media are mainlychemicals that are conveyed aboveground and combined with a well-defined set of operation conditions

regarding, for example, pressure, tem-perature and concentrations of media.Based on this, each application in the

various CPI segments can be lookedat as being a unique and sometimesquite-challenging case. Projects in theCPI typically require one or more ofthe following constraints for a pipingsystem [ 2]:

• Considerable safety margins or dry-running properties as a system

• Sufficient chemical resistance, orpredictable or manageable corrosion

• Uniform corrosion behavior of allcomponents with direct mediacontact

• Simple maintenance, extension orrestructuring of the system

• Attractive price/performance ratio• High level of availability of the

components• Availability of a steady growing pool

of longterm field references• Ease of installationCompared with other industries, the

application of pipe usage in the chemi-cal sector is characterized accordingto a demanding standard involvingsafety and an enormous knowledge ofactual field experience gained with agiven material in the specific processof interest.

This might account for why poly-mers remain a comparatively small

part — about 10% — of the globalCPI piping market [ 3]. However, look-ing at this from the perspective of amaterial scientist who is able to judgethe technical potential of the poly-meric materials in such a field of ap-plication, different and higher sharesshould be expected and the rate ofadoption is increasing.

Advantages & characterizationChemical resistance. The most deci-sive aspect for piping materials in thechemical sector is long-term chemicalresistance. It is rather self explanatorythat the chemical resistance profile of

Feature Report

32 CHEMICAL ENGINEERING WWW.CHE.COM SEPTEMBER 2010

Feature Report

FIGURE 2. These closeups (transmission mode; 1:200) of microtome cuts of

PVC-U piping-system components after six years of service (37 wt.% hydrochloricacid) demonstrate the importance of polymer formulation. The image at the left is forpremium industrial grade pipe, while that on the right is for a standard fitting; differ-ences of 100% in the corrosion attack are evident in the non-premium PVC-U

Stephan Schüßler

Georg Fischer DEKA GmbH

Attractive cost to

performance ratio

Availability, package

approach

Versatile jointing-

technology

Established quality assur-

ance and standardization

Variability of the

piping concept

Field references,

understanding of the

factors relevant for

performance

Wide range of chemical

resistance

FIGURE 1. Polymer-based pipingsystems deliver many

advantages, such asthose listed here

Polymer-Based Piping

Systems in the CPIIf properly used, polymeric piping and

components can be cost-effective alternatives

to those made of traditional materials



the respective polymer-based piping-system component will be stronglydefined by its chemical identity. How-ever, for a non-specialist it is not atall straight forward to accept that dif-ferent polymers show very large dif-ferences in their chemical resistanceprofiles. Additionally, this profile canbe influenced, shaped and adapted toa specific application when the impactof the polymer formulation is fully ex-ploited. Furthermore, the enormousinfluence on the polymer properties

and the chemical resistance can alsobe gained by the processing of theformulation. In some cases both as-pects can be of similar impact. Figure2 shows microtome cuts of unplas-ticized, polyvinyl chloride (PVC-U)piping components used in a typicalCPI application after several yearsof continuous service. This simple ex-ample illustrates the range of effectsof chemical resistance linked to theformulation of the polymer.Cost-to-performance ratio and

availability of the system components. When comparing polymer-based piping systems to alternativemetallic systems, a number of attrac-tive features of the former becomesevident: Low weight, thermal andelectrical insulating properties, oftensimpler jointing techniques, as wellas easier handling during installa-tion. Additional synergies regardingproject pricing are possible by exploit-ing the ability of some manufacturersof piping system components to offercomplete and harmonized systemsencompassing a wide range of dimen-sions and pressure ratings. Such sys-

tems also cover integrated solutionsof measurement and control units aswell as various valve systems. Thissynergistic aspect can even be furtherenlarged in cases where the manu-facturer is able to supply entire pip-ing systems for different applicationsalong with engineering or consultingsupport to the project. Figure 3 showsa good example of such a system fabri-cated out of polypropylene (PP).

As a rule, such standard systemscan always be adapted to individual

requirements (for example, regardingthe dimensions) by special customizingof units for the processors. This in turnis appreciated by the CPI-users, andhas always been a strong argument forthe use of polymers in CPI piping.

The various components of such sys-tems are usually backed by a power-ful logistic system that enables globalavailability. In general, they are glob-ally compatible to the respective prod-ucts of different vendors as long as im-perial and metric sizes are not mixed.

Fabrication is usually based on therespective standards (ISO EN, DINor ASTM), and within a given systemyou may find a harmonization of geo-metrical tolerances. Established man-ufacturers also take care that specialapprovals will cover the entire rangeof relevant system components. Forfurther reading in this field, see Ref. 4on planning fundamentals.

Multiple jointing Jointing of polymer-based-piping sys-tem components is quite versatile andsubjected to the choice of the poly-mer. Established approaches from the

draining, sewage and utility segment,such as removable socket joints (push-fit-fitting), clamping or using electrofusion are not utilized in chemical,petrochemical and other sectors of theCPI. In these application areas, ther-mal welding and solvent jointing arepredominant; in case of removable andmultiple jointing (for example, prefab-ricated spools), the use of flanges hasbecome state of the art — especiallyfor jointing of spools made out of dif-ferent materials.

Welding. The welding of polymer pip-ing in the CPI is split into socket-,butt-, fusion- and rod-welding, wherethe former two approaches are used forpure thermoplastic-pipe welding, andthe latter two are established in thefield of fiber-reinforced thermoplasticpiping (so-called dual laminates).

For butt-fusion methods there is achoice between simple contact (hotplate) and non-contact (infrared [IR])welding. Using IR welding has the ad-

vantage (among others) of a decreased

formation of welding beads due tothe reduced volume of the polymerbeing heated. A “beadless” weld canbe achieved by the so-called bead-andcrevice-free (BCF) welding processthat has widely been accepted as a

jointing standard in the pharmaceuti-cal and semiconductor industries (seeFigure 4).Cementing. For solvent-cement joint-ing, various solvent-based glues areused; the respective formulations arefine-tuned to match the individualrequirements defined by the polymerand the field of application. It is worthnoting that this technique has also

CHEMICAL ENGINEERING WWW.CHE.COM SEPTEMBER 2010 33

FIGURE 3.In addition topiping, somevendors also

offer a compre-hensive line of

components.

Those shownhere are for aPP pressure-

piping system



Feature Report


reached the state that jointingof PVC-U, for instance, can bedone with a special solvent ce-ment that is even able to cope

with long-term and steady con-tact to strong oxidizers, such asconcentrated sulfuric acid.

As soon as the dimensions offabrication tolerances of pipesand fittings exceed a certainlimit, solvent-cement jointingbecomes no longer practicallyfeasible due to both the gapsthat need to be “bridged” andthe procedure of assembly (re-quired forces, application ofthe cement and so on). In all

those cases the dual laminates(based on welding and flang-ing) are then widely acceptedas an alternative. Note that nosolvent-cement jointing is rec-ommended in the field of duallaminates.

QA and standardizationSince the market introductionof polymer-piping systems afew decades ago, many national stan-dards (for instance, DIN in Germany

or ASTM in the U.S.) have been elabo-rated, continuously developed andstepwise accepted — also globally inmany cases. Nevertheless, standard-ization of polymer-piping systemsis completed by international ap-plication norms which are updatedregularly by international competentworking groups. For selected applica-tions (such as drinking water or gassupply) additional approvals com-bined with external third-party test-ing supervised by a separate quality

assurance body (for example, the DINCertco in Germany) do effectivelyincrease the quality level of such ap-proved piping systems. As a rule, suchapprovals are based on even stricternational quality-assurance (QA) reg -ulations (such as various DIN Certcoguiding rules). For the global CPI itis very important to consider that theso- called German Institute for Build-ing technology (DIBT; Berlin; www.dibt.de) provides a unique, worldwideapproval based on such QA guide-lines. This DIBT approval is the basisfor a very narrow-meshed testing pro-gram and documentation of each lot of

piping products. In particular, whilesetting a strong priority on the com-

mitment to a clearly defined materialformulation — to be disclosed to theDIBT by a non-disclosure agreement(NDA) and an integrated third-partytesting procedure — approved prod-ucts are also linked to a comprehen-sive chemical-resistance list that willalso provide additional safety factors(distinguishing between temperatureand media concentration) for appro-priate dimensioning of the piping sys-tem. Thus, this DIBT-approval shouldbe considered as much more than just

a national German QA issue; it israther a very helpful specification toolfor end-userss making use of polymer-based piping systems for conveyanceof hazardous chemical media.

In addition to its presence in thestandards of the American Weldingsociety (AWS), the jointing of suchsystems is documented and updatedin comprehensive detail by the guide-lines issued by the German WeldingSociety (DVS) [5]. Similar to the fab-rication standards of polymer-pipingsystem components, these guidelineshave been globally accepted overmany years, laid down in many end-

user specifications and are continu-ously being updated and completed.

Furthermore, the regular trainingand education of polymer-welders isbased on these standards. Note thata given DIBT pipe approval does di-rectly refer to the respective DVSguidelines regarding planning, con-struction and joining of the respec-tive piping products. Thereby, addi-tional support is given to keeping upwith quality.

In addition, many competent end-users (typically bigger companies inthe CPI) rely on the use of a sensi-

ble and in-house developed systemof standards, which are also part oftheir respective process specifica-tions. Of course, these internal andindividual standards are also regu-larly reviewed and updated based ona steady growing experience gainedfrom practical long-term use of poly-mer piping systems.

Versatile piping conceptThere is no other class of materialshowing a larger variety of piping con-cepts available for CPI applicationsthan polymer pipes. Table 1 presentsa number of these.

TABLE 1. THE VERSATILITY OF POLYMER-PIPING SYSTEMS

Concept Jointing technology TypicalOD-range /mm

Characteristics

Thermoplasticpressure pipe

(Butt-fusion) welding;solvent cement joint-ing, flanging

16 – 2,000 Standard in the CPI

Doublecontainment

Solvent cementjointing;butt-fusion welding

20 – 225(Inner pipe)

Increased safety due topipe-in-pipe concept; outershell frequently made oftransparent PVC-U

Duallaminates

Welding (butt fusion /rod); flanging

16 – 2,000 Increased safety due topipe-in-pipe concept; sig-nificant increase of therange of applicability as thethermoplastic inliner is onlyused as the “chemical bar-rier”; all mechanical loadis handled by the externalFRP-layer

Tubes Push-fit sockets, flar-ing, screwing, custom-ized solutions

< 2 in. Coiled tubing made, forexample, from full fluori-nated polymers used indouble containment pipingare of particular interest

for very demanding CPI-applications (for instance,electronic-grade chemicalmedia handling)

Ventilationpipes

Socket jointing incombination with sol-vent cement joiningor (rod-)welding

< 800 Frequently the only econom-ical alternative to handlecorrosive exhaust fumes

Customizedpiping

Multiple and veryindividual

Usually< 250

Pipes as semi-finishedproducts; mostly no system-concept required



CHEMICAL ENGINEERING WWW.CHE.COM SEPTEMBER 2010 35

A good investment over decades Although polymer-based piping sys-tems have not reached the status

of metal-based piping in CPI usage,there are a variety of quite demand-ing segments in CPI where the spe-cific advantages of polymer pipes havebeen understood, systematically andsuccessfully exploited for many yearsnow [6]. The global chlorine industry,basic-chemical synthesis, logistic part-ners for chemical media, surface tech-nologies (for example, galvanizing andpickling industry), pulp and paper,as well as power plants are the mostimportant fields of application. The

combination of the practical experi-ence gained from these sectors and theknowledge derived from other fields ofapplication leads to a considerable poolof data supporting the assessment andfurther understanding of the longtermperformance as well as to assist in thedecision making for material selec-tion. The continuous evolution of thatknowledge-pool is efficiently supportedby both an active international net-work of polymer-corrosion specialistsas well as international and national

joint efforts in polymer-corrosion re-search of institutes, universities andindustry-partners. In this concern theimmense contribution (30 years of ac-tive research) of the Swerea KIMAB(former Swedish Corrosion Institute,SE) as well as the recent activities ofthe NACE (U.S.), Eurocorr (EU), FGK/ GfKorr and KRV (Germany) should berecognized. The result of this work isprimarily a steadily increasing poolof longterm-field references, thor-oughly evaluated case studies of keyapplications as well as the buildup ofsystematic databases to extrapolateor forecast the corrosion process of a

given polymer in contact with chemi-cal media under varying service condi-tions. Figures 5 and 6 provide an im-

pressive example of the status of suchefforts in this field.

Physical and natural barriers A comparatively high thermal expan-sion, longterm creeping under me-chanical load as well as a significantreduction of mechanical propertiesunder increasing temperature are thewell-known, inherent shortcomings ofpolymers that have to be consideredin any polymer-product application.Those processes are, of course, well-

understood, and corresponding ma-terial data are always considered inthe material selection, design anddimensioning. Polymer-specific safetyfactors and very reliable data toquantify the longterm creep behaviorsupport this selection process. Whenusing smaller pipe-dimensions (O.D.typically < 110 mm) in the CPI, manyexperienced end-users specify the ap-plication of thick-walled piping sys-tems for safety reasons (for instance,pipe series 9 for PVC-U). As already

mentioned, the use of dual laminatesfor handling of chemical media at el-evated temperatures or higher pres-sure (or both) is also a widely appliedtool to fully exploit the potential ofchemical resistance properties of agiven polymer and to surmount someof the polymer-inherent shortcom-ings. Keeping a proper bonding of theinliner to the FRP sleeve maintainedas well as not exceeding the criticalwall-thickness of the inliner are nec-essary preconditions to guarantee asafe operation.

The energy-transporting propertiesof polymers can strongly be influenced

by compounding with suitable func-tionalizing additives; by doing so, evenan increase of the thermal conductiv-

ity of a few orders of magnitude underretention of the electrical insulation-properties is possible.

The non-destructive monitoring ofcorrosion processes in polymer pip-ing is still an unfulfilled demand ofmany end-users and the realizationof such a concept is currently not insight. However, efficient managementof corrosion knowledge, practical expe-rience, a rational understanding of thechemical processes and materials in-

volved can already give a good and re-

liable basis for a sustainable and safeoperation. Competent manufacturersare always good partners for the end-customer in case of need.

Quo vadis industrial piping ?Despite being a small branch of theindustry, industrial piping and pip-ing for the CPI have always been

very innovative. During the last fewyears, the impulse for innovation inthe chemical industry shows a focusat the site of compounder and pro-

cessors rather than at the site of theraw material suppliers. In the field ofmaterials and piping concepts, a trendtowards more pressure-resistant andstiffer pipes has become evident. The

various approaches are quite versatileand cover innovations such as layeredstructures, continuous welding of ori-ented polyolefin tapes on polyolefinpipes made from the same polymer;and the use of innovative copolymersor fillers, to name just a few. The topics“functional layers” and “nano-technol-ogy” have just emerged in practicallyrelevant concepts for this type of in-dustry and are expected to strongly

FIGURE 4. Shown here is view of aBCF weld of PVDF (polyvinylidene fluo-ride). The energy for melting the poly-mer is introduced from the outside; theformation of a crevice-free and smoothinner surface in the joining region isachieved by temporarily inserting a bal-loon filled with compressed air

FIGURE 5. After 17 years of continu-ous contact with 35 wt.% hydrogen per-oxide (25°C), only 60 µm of corrosionattack is measured with PVC-U pipingcomponents. Such minor traces of cor-rosion do not influence the function orsafety of the system at all

FIGURE 6. This graph show the isothermaldiffusion coefficients of mixed acid (HNO3 / HF; T= 65°C) with variable concentration(wt.%) in PVC-U determined from the combi-nation of laboratory-scale immersion testingand simulations (source: Swerea KIMAB [7])

201918171615HNO3

H F

8.0 0.1243

0.07630.0883

0.0943

0.1003

0.1063

0.1123

0.1183

7.5

7.0

6.5

6.0

5.5

5.0

4.5

4.0

1413121110

0.0823



Feature Report


influence the innovation in this fieldin the course of the coming years.

With regard to the jointing of poly-mer piping, the butt-fusion welding of

PVC-U and C-PVC (post-chlorinatedPVC) is currently established as analternative to the conventional sol-

vent-cement jointing of these typesof materials.

Concluding remarksPolymer-based piping systems havebeen used with great success in theCPI for many years now. The varioussystems that are currently availablein the market are capable of cover-

ing practically any CPI applicationinvolving temperatures up to 100°Cand pressures to 10 bar. In largerprojects, tremendous advantages in

cost versus performance can be ex-ploited when fully considering that

various polymer-based piping sys-tems for different applications withina given project may be available fromone manufacturer.

A well-developed standardizationeffort coupled with an effective QAof the products and an individuallyelaborated specification by the end-user will contribute to further growthof the use of polymer based piping

systems in the CPI. Innovation anda steadily growing understanding ofthe supply chain regarding longtermperformance and corrosion details of

polymer pipes are expected to sup-port this process. ■

Edited by Gerald Ondrey

Circle 34 on p. 62 or go to adlinks.che.com/29254-34

AuthorStephan Schüßler is head ofR&D at Georg Fischer DEKAGmbH (GF DEKA; Kreuz-straße 22, 35232 Dautphetal-Mornshausen, Germany.Phone: +49-64-68951-131;Fax: +49-64-68915-29131;Email: stephan.schuessler@ georgfischer.com). As thefocus of GF DEKA is on poly-mer piping systems for CPIapplications, his material and

product development projects are strongly re-lated to polymer corrosion issues and new fields ofapplications for polymer piping. He also contrib-utes to technical marketing, and represents thecompany in various national and internationalexpert-circles as well as authoring publicationsin the field of polymer piping. Schüßler stud-ied at the Philipps University (Marburg/Lahn,Germany) and the School of Chemistry (Bristol,U.K.), and received a Diplom in chemistry (poly-mer chemistry). He received a Ph.D. (physics andpolymer chemistry) in 1995, followed by a year offull-time marketing education.

References1. Georg Fischer AG; 50 years of know-how in

plastics, Schaffhausen, Switzerland, 2006.

2. Schüßler, S.; “Kunststoff-Industrierohre –Gründe genug für eine eigene Klasse”; KRV-Nachrichten, Bonn, Germany, January 2004.

3. GFKorr Jahrestagung 2005; Dechema e.V.,Frankfurt, Germany, November 2005.

4. Georg Fischer AG, Planungsgrundlagen fürindustrielle Rohrleitungssysteme, Schaff-hausen, Switzerland, 2006.

5. Taschenbuch DVS-Merkblätter und –Richtlin-ien, Beuth Verlag, 12. Auflage, Berlin, 2008.

6. Nowack, E. others “60 Jahr Erfahrungen mitRohrleitungen aus weichmacherfreiem Poly-

vinylchlorid (PVC-U)”; KRV-NachrichtenJanuary 1995.

7. Römhild, S., Influence oft the material charac-teristics on the resistance to pickling acids,presentation T 5-Meeting Swerea KIMAB;Stockholm, December 2008.

Polymer-Based Piping Systems in the CPI

Documents

Transcript of Polymer-Based Piping Systems in the CPI